As particulate rubbers, SBR, NBR, CR and EPDM are commercially available. These are made particulate mainly for continuously mixing rubber and a variety of compounding agents when vulcanized rubbers are produced, and have a particle diameter as large as about 0.4 mm to about 4 mm. However, in the field of modifiers for rubber or plastics, as well as fillers, additives for ink or cosmetics, etc., a fine particulate rubber compounding agent has been sought after from a viewpoint of rubberyness, lightweight properties, and so on.
Studies for fining the particle size have been made in respect of EPDM. For example, U.S. Pat. No. 4,294,744 reports such fine EPDM, but the particle diameter thereof ranges from 500 to 3000 .mu.m, which lies outside the territory of a fine particulate rubber.
Thus, to the knowledge of the present inventors, a fine particulate amorphous copolymer which has fine particulates, and wherein crosslinkages are formed in the particles, is not known.
On the other hand, thermoplastic elastomers are used as energy saving or resource saving type elastomers, in particular, as substitutes for vulcanized rubbers, for automobile parts (such as bellows, tubes, interior sheets and mudguards), industrial machine parts (such as pressure hoses, gaskets and diaphragms), electronic or electric equipment parts, construction materials, etc. For example, olefin series thermoplastic elastomer compositions comprising a blend of completely crosslinked ethylene/propylene/non-conjugated diene copolymer rubber (EPDM) and polyolefin are known in the art as disclosed in Japanese Examined Patent Publications (Kokoku) Nos. 46138/1983, 18448/1980, etc. These compositions have excellent properties, but are limited as a substitute for vulcanized rubber because of a lack of rubberyness and moldability, an improvement of which is required.
Also, polyesters mainly comprised of polyethylene terephthalate and polybutylene terephthalate have an excellent high elasticity, low creep, low water absorption, chemical resistance, high softening point, high electric insulation, etc., and are therefore widely used as fibers or films, as well as engineering plastics for machine parts or electric parts. But although the polyesters of this sort have the excellent properties as mentioned above, they do not have a sufficiently high impact resistance, such as the notched Izod impact strength, and are disadvantageous in that they are not suitable for molded parts requiring high impact resistance. Accordingly, efforts have been made to improve the impact resistance without impairing the above-mentioned excellent properties inherent to polyesters.
As attempts to improve the impact resistance of polyesters, there have been reported a process in which butyl rubber is mixed into polyester (see Japanese Patent Publication No. 5224/1970) and a process in which ethylene/propylene rubber is mixed into polyester (see Japanese Patent Publication No. 5225/1971). Both of these, although showing an improved impact resistance, have a drawback in that the improvement is small, or the modulus is lowered.
Several attempts have been made to obtain thermoplastic resins having excellent weathering resistance, impact resistance, surface gloss and so on by graft polymerization of an .alpha.-olefin copolymer rubber or an ethylene/.alpha.-olefin/polyene copolymer rubber with an alkenyl aromatic compound and a vinyl monomer copolymerizable therewith. For instance, Japanese Patent Publication (Kokoku) No. 16394/1968 discloses a process in which the above rubber components kept in the state of a latex are allowed to gel in the presence of a crosslinking monomer such as divinylbenzene, followed by graft copolymerization to obtain a thermoplastic resin, and Japanese Patent Publication (Kokoku) No. 35718/1973 discloses a process in which the above rubber particles in a latex are swollen with a liquid aliphatic hydrocarbon or alicyclic hydrocarbon, followed by graft copolymerization as they are.
However, none of the processes in the known prior arts have obtained a thermoplastic graft copolymer resin having a weathering resistance, impact resistance, surface gloss, etc. reaching levels satisfactory for practical use.